The present invention relates to railway braking systems, and more particularly to combined electronic and pneumatic braking systems for railway freight trains.
Railway freight braking systems traditionally have utilized a pneumatic brake system that is operated pneumatically and in which the control functions are obtained through utilization of pneumatic valves. These braking systems include a brake pipe for pneumatic communication between the locomotive and each individual car in the train. The pneumatic brake pipe has been utilized in a multi-function role, including charging reservoirs on-board each individual freight car; instituting brake applications; and controlling the release of the brakes on the train. Such systems utilize on-board pneumatic control valves such as, for example, ABD, ABDW, ABDX, or DB-60 valves on each freight car. Such cars can operate with pneumatic 26 TYPE Locomotive brake equipment or microprocessors types like EPIC equipment supplied by Westinghouse Air Brake Company. In these systems the level of desired brake pressure can be controlled by the pressure in the brake pipe which is controlled from the locomotive. An advantage of this type of system is the utilization of a single pneumatic communication, the brake pipe, running the length of the train.
Electronically controlled pneumatic (ECP) freight train braking systems are now being developed for long freight trains. In ECP brake systems, the role of the conventional pneumatic control valve can be replaced by an electronic controller which governs solenoid actuated valves on each car that control the brake operation. The electronic controller on each car can receive electrical command signals from the locomotive for controlling the braking functions of each car. Until recently, utilization of electrical command signals from a locomotive to control brake operation has been employed mainly in passenger trains and transit equipment, on relatively short trains. Conventionally, an electrical command signal is sent from the locomotive through the length of the train, with the signal level controlling both the propulsion and the desired amount of braking. In the past, such ECP braking systems were not generally utilized in freight brake operations, however, due to advances in technology, such ECP system are becoming more feasible in freight brake operations. Because a majority of freight trains can still use only the conventional pneumatic braking system, rail cars having an ECP system can frequently also include a pneumatic control valve. Such a combined system can be desirable so that the railcar can be used in either the newer ECP systems or the conventional pneumatic system, which is presently still the most prevalent type of freight train braking system.
In a typical such ECP combined freight train braking system having separate auxiliary and emergency reservoirs, the electronic controller governs two solenoid actuated brake application valves. One of the valves is connected between the auxiliary reservoir and a brake cylinder and the other is connected between the emergency reservoir and the brake cylinder. The electronic controller can also control a release valve connected to the brake cylinder for venting the brake cylinder to the atmosphere to release the brakes. In response to a command signal, the electronic controller can initiate service or emergency braking applications, or implement a release of the brakes. In such braking systems, where an electronic controller is utilized to control pneumatic equipment, the conventional practice has been to employ two separate brake application valves, one controlling the application of pressure from the auxiliary reservoir and one controlling the application of pressure from the emergency reservoir.
Two separate brake application valves are conventionally used to prevent the transfer of pressure between the separate reservoirs. Additionally, when a pneumatic control valve is included in the system, a separate brake application valve for each reservoir can be required for an ECP system to work properly because the pneumatic control valve relies on separate reservoirs to distinguish between maximum service and emergency brake cylinder pressures.
With electronic brake control it is possible to combine the separate auxiliary and emergency reservoirs into a single large reservoir, because the maximum brake cylinder pressure for service and emergency applications can be limited by the electronic processor. In this case, a single application solenoid may be employed to admit the air from the unified reservoir to the brake cylinder to apply the brakes.
Accordingly, there is a need for a combined electronic and pneumatic freight train braking system wherein the electronic controller can employ a single brake application valve instead of the previously utilized two brake application valves. Such a brake control system must properly and reliably control the braking functions on each car during both service and emergency braking applications, including whenever a pneumatic control valve is also a part of the system.